1. Field of the Invention
The present invention relates to a satellite broadcast reception converter that constitutes the basis of a satellite broadcast reception system together with an antenna and a tuner. More particularly, the present invention relates to a satellite broadcast reception converter having an internal structure by which an output return loss is reduced.
2. Description of the Prior Art
The satellite broadcast reception converter (hereinafter referred to as an LNB) is fed with faint radio wave signals in a high-frequency band received by an external parabola antenna from a satellite, amplifies the signals thus fed in, converts the signals into output signals (hereinafter referred to as IF signals) in an intermediate frequency band (a range between approximately 950 MHz and 1700 MHz has been a band commonly used in recent years) for easy handling, and feeds out the output signals to an external tuner.
A conventional LNB having the above-mentioned functions is generally formed with a chassis or a case 1 as an external structure as shown in FIGS. 7 and 8. Arranged at one end and another end of the LNB respectively so as to protrude outward therefrom are a primary reflector 2 into which a radio wave received by an unillustrated parabola antenna is guided and an F-type connector as an output terminal 3 to be connected to an unillustrated tuner with a coaxial cable or the like. Furthermore, a circuit board 4 is provided, inside the case 1, within a region between a rear side of the primary reflector 2 and an area adjacent to the output terminal 3. One end portion 4a of the circuit board 4 is connected to the output terminal 3 by way of an F-type line or a lead wire 5 and another end portion 4b is connected to the primary reflector 2. As can be seen, inside the case 4, sizes of the case 1 and the circuit board 4 are substantially identical in plan view.
With advancement in integration technologies that enable miniaturizations of circuit components and circuit patterns arranged on such a circuit board as the circuit board 4, and in an attempt to reduce the cost in materials by effectively utilizing these technologies, recent trends show that a circuit board such as the circuit board 4 has been reduced in size. In this case, for example as shown in FIG. 9, a circuit board 14 is arranged within the case 1 in such a way that another end portion 14b thereof can be connected to the rear side of the primary reflector 2. Consequently, one end portion 14a of the circuit board 14 is located remotely from the output terminal 3, and said one end portion 14a is connected to the output terminal by way of an extended lead wire 15.
Here, by comparing FIG. 7 and FIG. 8, it is understood that the size of the case 1 remains unchanged and that the primary reflector 2 and the output terminal 3 are so positioned as to keep a predetermined distance from each other. In this arrangement, it is possible to share the same LNB among different products by fixing the position of the LNB relative to the parabola antenna. The LNB, in general, is fixed relative to the antenna with a fixing tool by making the output terminal 3 as a fixing base. Because of this reason, if the distance between the primary reflector 2 and the output terminal 3 differs from product to product, a focal point of the primary reflector 2 changes accordingly.
Here, such an LNB as the one shown in FIG. 9 has a longer lead wire 15 that induces unnecessary inductance components therearound which prevent a proper impedance matching from being taken. As a result, the output return loss of the IF signals, an indicator of the basic performance of the LNB, is worsened.
Conventional technologies for improving the problem like this include one that provides an earth portion integrally formed within the case 1 or a ground component in the case 1 so that the earth portion or the ground component is placed in close proximity to the lead wire 15 (for example, the Japanese Patent Application Laid-Open No. 2000-252709, page 2 to page 4 and FIG. 1 to FIG. 3). According to this improved technology, capacitive components that are induced between the lead wire 15 and the earth portion or the ground component prevent unnecessary inductance components from being induced. Consequently, it is possible to take a proper impedance matching and, thereby, at least improve the output return loss of the IF signals.
However, according to the aforementioned conventional improved technology, it is necessary to secure an infinitesimal distance between the lead wire 15 and the earth portion or the ground component. To achieve this, it is imperative to devise a practical method at a designing stage such as covering the lead wire 15 with an insulating tube or at a manufacturing stage such as improving dimensional accuracy. Moreover, this technology has a drawback of making inside the case 1 complicated.